Certain electronic devices, such as STT RAM, require that a plurality of rings of a magnetoresistive stack be deposited on a substrate. These rings have been previously formed by ion beam milling which creates the center hole for the ring. Ion beam milling, however, suffers from a number of disadvantages.
One disadvantage of the ion beam milling is that the process is serial and, for that reason, very slow in manufacturing time. Such ion beam milling also leads to the redeposition of the magnetic tunnel junction material on the nanoring surface which leads to shorting of the device.
Another process that is currently used to create the rings of magnetoresistive material on the substrate for STT RAM involves the reactive ion etching of the magnetic tunnel junction. In this method, methanol is used to assist with the etching process. A primary disadvantage of this process, however, is that it is only possible to etch 20-30 nm in the vertical direction with this process. With an STT RAM application, however, that is insufficient.
A final process that is currently used to form the rings of magnetoresistive material for STT RAM involves the use of polystyrene nanospheres. In particular, it has been shown that it is possible to define the center hole of the nanoring using an ordered array of nanospheres. However, in practice it has proven difficult to obtain an ordered array on a large-scale area. Instead, the nanospheres tend to be arranged in a hexagonal array that is less than ideal for forming the contacts involving random access memory, such as STT RAM.